In magnetic recording, superparamagnetic instabilities become an issue as the grain volume of the recording media is reduced in order to control media noise for high areal density recording. The superparamagnetic effect is most evident when the grain volume V is sufficiently small that the inequality KuV/kBT>70 can no longer be maintained, where Ku is the material's magnetic crystalline anisotropy energy density, kB is Boltzmann's constant, and T is absolute temperature. When this inequality is not satisfied, thermal energy demagnetizes the stored bits. Therefore, as the grain size is decreased in order to increase the areal density, a threshold is reached for a given material Ku and temperature T such that stable data storage is no longer feasible.
Conventional magnetic recording techniques will likely reach physical limits to storage density which are due to the super-paramagnetic effect. One possible solution to overcome this limit is heat assisted magnetic recording (HAMR). Heat assisted magnetic recording generally refers to the concept of locally heating a recording medium to reduce the coercivity of the recording medium so that the applied magnetic writing field can more easily direct the magnetization of the recording medium during the temporary magnetic softening of the recording medium caused by the heat source. Heat assisted magnetic recording allows for the use of small grain media, which is desirable for recording at increased areal densities, with a larger magnetic anisotropy at room temperature to assure sufficient thermal stability. Heat assisted magnetic recording can be applied to any type of magnetic storage media, including tilted media, longitudinal media, perpendicular media and patterned media.
Extremely small thermal spots with high temperatures are required in a HAMR system to reduce the coercivity of the medium. To achieve such thermal spots, a focused optical beam from a laser with extremely high transmission efficiency is needed. Several optical transducers have been proposed to achieve high transmission efficiencies in small spots, however, numerical simulations suggest that the transmission efficiency of these optical transducers may not be large enough to achieve high temperatures in extremely small spots.
There is a need for recording media that can be used in heat assisted magnetic recording systems and provides an increased storage density.